A mob torched a Kenyan church on Tuesday, killing villagers cowering inside, as the death toll from ethnic riots triggered by President Mwai Kibaki's disputed re-election soared to nearly 200.
The opposition said around 250 people had died.
In the most grisly incident, about 30 people died when fire engulfed a church near Eldoret town where scores of Kibaki's Kikuyu tribe had taken refuge in fear of their lives.
The attack revived traumatic memories in east Africa of the slaughter in churches of tens of thousands of victims of Rwanda's 1994 genocide, and the mass suicide of hundreds of Ugandan cult members in a church fire in 2000.
Police, reporters and a senior security official said the blaze at the Kenya Assemblies of God Pentecostal church was deliberately started by a gang of youths.
Witnesses said charred bodies, including women and children, were strewn about the smoldering wreckage.
This is the first time in history that any group has attacked a church. We never expected the savagery to go so far, police spokesman Eric Kiraithe said.
Reinforcements were being rushed to the area to arrest all troublemakers regardless of their status in society, he said.
Our officers are exercising a lot of restraint in maintaining the law. This restraint will not last for ever.
Residents and a security source said the victims had sought safety at the church, about 8 km (5 miles) from Eldoret.
Some youths came to the church, said a local reporter from the scene. They fought with the boys who were guarding it, but they were overpowered and the youths set fire to the church.
The explosion of violence in one of Africa's most stable democracies and strongest economies has shocked the world and left Kenyans aghast as long-simmering tribal rivalries pitch communities against each other.
Leading local newspaper, the Daily Nation, feared Kenya was on the verge of a complete melt-down.
Police were out in force in the capital on New Year's Day, and the streets were quieter. But details emerged of a rising death toll and widespread destruction in one of the country's darkest moments since 1963 independence from Britain.
Washington first congratulated Kibaki -- then switched that line to express concerns about irregularities.
Britain, the European Union and others pointedly avoiding congratulating Kibaki, expressed concern, urged reconciliation and a probe into suspected voting irregularities.
The 2007 general elections have fallen short of key international and regional standards for democratic elections, the EU observer mission said in its formal assessment.
Western diplomats shuttled between both sides, trying to start mediation. British Prime Minister Gordon Brown called Kibaki and his opposition rival Raila Odinga.
The government thinks they can wait this out, but we're not convinced, one diplomat in Nairobi told Reuters.
The Eldoret area where the church massacre took place is multi-ethnic but traditionally dominated by the Kalenjin tribe.
It suffered ethnic violence in 1992 and 1997 when hundreds of mainly Kikuyus were killed and thousands more displaced.
A senior security official in Rift Valley said that as many as 15,000 people were now sheltering from the latest violence in churches and police stations in Eldoret.
He blamed the opposition for incitement.
We have lived together for years, we've intermarried, we have children, but now they've asked them to turn against them, the security official said. We don't do this in Kenya. It is what happens in Yugoslavia and Sudan.
An Irish Catholic priest in Eldoret, Father Paul Brennan, told Reuters vigilante gangs were roaming the streets.
Houses are being burned. It is too dangerous to go outside and count the dead, he said. The churches are full. There are four to five thousand in the main cathedral.
Most deaths have come from police firing at protesters, witnesses say, prompting accusations from rights groups and the opposition that Kibaki had made Kenya a police state.
Police gave a national death toll of 143 at midday.
Local media gave figures of between 153 and 164 at the same time. And Reuters reporters around Kenya estimated about 200 dead by late afternoon, with that number sure to rise.
Odinga said his Orange Democratic Movement (ODM) verified 160 fatalities to Monday night, but with overnight killings added, the total would likely be about 250 or slightly more.
(Additional reporting by Nicolo Gnecchi, Duncan Miriri, Helen Nyambura-Mwaura, Patrick Muiruri, Bryson Hull, Florence Muchori, Joseph Sudah, Andrew Cawthorne; and Guled Mohamed in Kisumu, Editing by Andrew Cawthorne)